Laser cladding is a promising photon-based surface engineering technique broadly utilized for fabricating harder and wear resistant composite coatings. In spite of excellent properties, the practical applications of l...Laser cladding is a promising photon-based surface engineering technique broadly utilized for fabricating harder and wear resistant composite coatings. In spite of excellent properties, the practical applications of laser claddings are relatively restricted when compared with well-established coating techniques because of their inherent defects identified as cracks, pores and inclusions. Substantial evidence suggests that the incorporation of an appropriate amount of rare earth in laser claddings can remarkably prevent these defects. Additionally, the presence of rare earth in laser claddings can notably enhance tribo-mechanical properties such as surface hardness, modulus of elasticity, fracture toughness, friction coefficient and wear rate. In this literature review, the effect of rare earth in reducing dilution and cracks susceptibility of laser claddings in addition to microstructural refinement attained was examined. Mechanical and tribological properties of these claddings along with their underlying mechanism were discussed in detail. Finally, this article summarizes current applications of laser claddings based on rare earth and was concluded with future research directions.展开更多
Sliding wear tests of chilled cast iron tappet-disc and cam-ball tribo-partners were conducted by using ball on disc testing device. Magnetron sputtering CrTiAlN hard coating and Graphite like carbon (GLC) solid lubri...Sliding wear tests of chilled cast iron tappet-disc and cam-ball tribo-partners were conducted by using ball on disc testing device. Magnetron sputtering CrTiAlN hard coating and Graphite like carbon (GLC) solid lubricant coatings were applied on either one or both of the contact surfaces on tribo-partners. Ball crater device and scanning electron microscope were used to investigate surface wear of rubbed track on disc and wear scar on ball. The sliding performances of tribo-partners were evaluated in terms of coefficient of friction at sliding surfaces and specific wear rate (SWR) on both of the rubbed surfaces under specific test conditions. All test results showed that GLC solid lubricant coating on both surfaces of tappet-disc and cam-ball was the best option to allow this tribo-partners having high performance in terms of sliding under high load with low coefficient of friction and low SWR. The advantage of using GLC solid lubricant coating is to enable mechanical parts made of ordinary and sustainable materials (e.g. cast iron or plain steels) to be operated under even harsher conditions of higher load and higher wear environment with improved performance.展开更多
On a self-developed circular-translation polishing machine,the influence of different electric potentials on the friction coefficient and wear properties of SiC/HT200 friction pair,which contacted as one electrode,wer...On a self-developed circular-translation polishing machine,the influence of different electric potentials on the friction coefficient and wear properties of SiC/HT200 friction pair,which contacted as one electrode,were studied in NaOH solutions.The results show that the friction coefficient of SiC/HT200 pair is 0.25 under no externally applied potential;but it decreases to 0.23 while applying +3 V polarization potential on the pair;in contrast,it increases to 0.30 when applying-3 V polarization potential on the pair.And the polished SiC surface under + 3 V potential is much smoother,while there are clear ploughing marks and adhesive region on the polished SiC surface under zero and-3 V potential,respectively.The mixed triboelectrochemical friction model has been proposed and the mechanisms of the electric effects on the tribological properties of SiC/HT200 friction pair in NaOH electrolyte are addressed.Results and discussion show that the anodic passivation technique may be used for hastening the running-in process of SiC/Fe friction pairs,as well as for polishing SiC to increase its materials removal efficiency while maintaining good surface quality.展开更多
Understanding the microstructural and tribo-chemical processes during tribological loading is of utmost importance to further improve the tribological behavior of metals. In this study, the friction, wear and tribo-ch...Understanding the microstructural and tribo-chemical processes during tribological loading is of utmost importance to further improve the tribological behavior of metals. In this study, the friction, wear and tribo-chemical behavior of Ni with different initial microstructures(nanocrystalline, bi-modal, coarse-grained) is investigated under dry sliding conditions. In particular, the interplay be-tween frictional response, microstructural evolution and tribo-oxidation is considered. Friction tests are carried out using ball-on-disk experiments with alumina balls as counter-bodies, varying the load between 1 and 5 N. The microstructural evolution as well as the chemical reactions beneath the samples’ surface is investigated by means of cross-sections. The samples with finer microstructures show a faster run-in and lower maximum values of the coefficient of friction(COF) which can be attributed to higher oxidation kinetics and a higher hardness. It is observed that with increasing sliding cycles, a stable oxide layer is formed. Furthermore, initially coarse-grained samples show grain refinement, whereas initially finer microstructures undergo grain coarsening converging towards the same superficial grain size after 2,000 sliding cycles. Consequently, the experimental evidence supports that, irrespective of the initial microstructure, after a certain deformation almost identical steady-state COF values for all samples are achieved.展开更多
Silicon carbide(SiC) can be tribo-chemically smoothened during a self-mated sliding procedure in the aqueous environment. As well reported in the point-contact tests, this smoothening process works well due to the abu...Silicon carbide(SiC) can be tribo-chemically smoothened during a self-mated sliding procedure in the aqueous environment. As well reported in the point-contact tests, this smoothening process works well due to the abundant water as oxidant. After this smoothening process, the tribo-surface is well polished, a closely mated tribo-gap naturally forms, and an ultra-low friction state is built. However, water in the tribo-gap could be insufficient in industrial applications, e.g., the seal gap in mechanical seals. In this study, the tribo-chemical smoothening behavior in such environment was researched. A surface-contact reciprocating test was used to simulate the aqueous environment where water was insufficient. After tests, compared to the published results from the point-contact tests, the same ultra-low friction state was achieved. A part of the tribo-surface was tribo-chemically smoothened. The obtained smoothened surface microstructure was consistent with the published information. Meanwhile, severe abrasive wear occurred. A porous oxygen-rich layer was found existing beneath the abrasion-induced grooves, in which numerous smashed wear debris adhered on the worn surfaces. We concluded that the shortage of water initiated the severe abrasion, meanwhile the generated wear debris aggravated the wear condition. This understanding is instructive for developing new methods to avoid the severe abrasion in the same water insufficient environment.展开更多
Lubricant on magnetic hard disk is essential to the stable lubrication at the head/diskinterface of the computer hard disk drive, The depletion phenomenon of the perfluoropolyalkylether(PFPE) lubricant ZDOL caused by ...Lubricant on magnetic hard disk is essential to the stable lubrication at the head/diskinterface of the computer hard disk drive, The depletion phenomenon of the perfluoropolyalkylether(PFPE) lubricant ZDOL caused by the head was investigated. FC722, a type ofpoly(fiuoroalkylmethacrylate) used as anti-wetting-agent (AWA) on the magnetic head, and its ef-fect on reducing lubricant depletion was study. Time-of-flight secondary ion mass spectrometer(TOF-SIMS) was used to characterize the lubricant ZDOL and AWA. TOF-SIMS results suggestthat the lubricant depletion should be due to dynamic friction between the magnetic head and diskduring the head flying or seeking over the disk surface, the amount of lubricant picked up by thehead varying with the different flying height. The AWA coating layer on head obviously reduces theamount of lubricant picked-up. The possible molecular interaction mechanics of AWA and ZDOLwith DLC overcoat of the head was discussed.展开更多
基金Project supported by the University of Malaya Research Grant(UMRG,RP013A-13AET)University of Malaya Research Grant(UMRG,RP035A-15AET)
文摘Laser cladding is a promising photon-based surface engineering technique broadly utilized for fabricating harder and wear resistant composite coatings. In spite of excellent properties, the practical applications of laser claddings are relatively restricted when compared with well-established coating techniques because of their inherent defects identified as cracks, pores and inclusions. Substantial evidence suggests that the incorporation of an appropriate amount of rare earth in laser claddings can remarkably prevent these defects. Additionally, the presence of rare earth in laser claddings can notably enhance tribo-mechanical properties such as surface hardness, modulus of elasticity, fracture toughness, friction coefficient and wear rate. In this literature review, the effect of rare earth in reducing dilution and cracks susceptibility of laser claddings in addition to microstructural refinement attained was examined. Mechanical and tribological properties of these claddings along with their underlying mechanism were discussed in detail. Finally, this article summarizes current applications of laser claddings based on rare earth and was concluded with future research directions.
文摘Sliding wear tests of chilled cast iron tappet-disc and cam-ball tribo-partners were conducted by using ball on disc testing device. Magnetron sputtering CrTiAlN hard coating and Graphite like carbon (GLC) solid lubricant coatings were applied on either one or both of the contact surfaces on tribo-partners. Ball crater device and scanning electron microscope were used to investigate surface wear of rubbed track on disc and wear scar on ball. The sliding performances of tribo-partners were evaluated in terms of coefficient of friction at sliding surfaces and specific wear rate (SWR) on both of the rubbed surfaces under specific test conditions. All test results showed that GLC solid lubricant coating on both surfaces of tappet-disc and cam-ball was the best option to allow this tribo-partners having high performance in terms of sliding under high load with low coefficient of friction and low SWR. The advantage of using GLC solid lubricant coating is to enable mechanical parts made of ordinary and sustainable materials (e.g. cast iron or plain steels) to be operated under even harsher conditions of higher load and higher wear environment with improved performance.
基金Sponsored by the National Natural Science Foundation of China(Grant No.51475119)the National Program on Key Basic Research Project of China(Grant No.2011CB013202)
文摘On a self-developed circular-translation polishing machine,the influence of different electric potentials on the friction coefficient and wear properties of SiC/HT200 friction pair,which contacted as one electrode,were studied in NaOH solutions.The results show that the friction coefficient of SiC/HT200 pair is 0.25 under no externally applied potential;but it decreases to 0.23 while applying +3 V polarization potential on the pair;in contrast,it increases to 0.30 when applying-3 V polarization potential on the pair.And the polished SiC surface under + 3 V potential is much smoother,while there are clear ploughing marks and adhesive region on the polished SiC surface under zero and-3 V potential,respectively.The mixed triboelectrochemical friction model has been proposed and the mechanisms of the electric effects on the tribological properties of SiC/HT200 friction pair in NaOH electrolyte are addressed.Results and discussion show that the anodic passivation technique may be used for hastening the running-in process of SiC/Fe friction pairs,as well as for polishing SiC to increase its materials removal efficiency while maintaining good surface quality.
基金the EFRE Funds of the European Commission for support of activities within the AME-Lab projectfinancial support from the Deutsche Forschungsgemeinschaft (DFG, project ID: SU 911/1-1)
文摘Understanding the microstructural and tribo-chemical processes during tribological loading is of utmost importance to further improve the tribological behavior of metals. In this study, the friction, wear and tribo-chemical behavior of Ni with different initial microstructures(nanocrystalline, bi-modal, coarse-grained) is investigated under dry sliding conditions. In particular, the interplay be-tween frictional response, microstructural evolution and tribo-oxidation is considered. Friction tests are carried out using ball-on-disk experiments with alumina balls as counter-bodies, varying the load between 1 and 5 N. The microstructural evolution as well as the chemical reactions beneath the samples’ surface is investigated by means of cross-sections. The samples with finer microstructures show a faster run-in and lower maximum values of the coefficient of friction(COF) which can be attributed to higher oxidation kinetics and a higher hardness. It is observed that with increasing sliding cycles, a stable oxide layer is formed. Furthermore, initially coarse-grained samples show grain refinement, whereas initially finer microstructures undergo grain coarsening converging towards the same superficial grain size after 2,000 sliding cycles. Consequently, the experimental evidence supports that, irrespective of the initial microstructure, after a certain deformation almost identical steady-state COF values for all samples are achieved.
文摘Silicon carbide(SiC) can be tribo-chemically smoothened during a self-mated sliding procedure in the aqueous environment. As well reported in the point-contact tests, this smoothening process works well due to the abundant water as oxidant. After this smoothening process, the tribo-surface is well polished, a closely mated tribo-gap naturally forms, and an ultra-low friction state is built. However, water in the tribo-gap could be insufficient in industrial applications, e.g., the seal gap in mechanical seals. In this study, the tribo-chemical smoothening behavior in such environment was researched. A surface-contact reciprocating test was used to simulate the aqueous environment where water was insufficient. After tests, compared to the published results from the point-contact tests, the same ultra-low friction state was achieved. A part of the tribo-surface was tribo-chemically smoothened. The obtained smoothened surface microstructure was consistent with the published information. Meanwhile, severe abrasive wear occurred. A porous oxygen-rich layer was found existing beneath the abrasion-induced grooves, in which numerous smashed wear debris adhered on the worn surfaces. We concluded that the shortage of water initiated the severe abrasion, meanwhile the generated wear debris aggravated the wear condition. This understanding is instructive for developing new methods to avoid the severe abrasion in the same water insufficient environment.
文摘Lubricant on magnetic hard disk is essential to the stable lubrication at the head/diskinterface of the computer hard disk drive, The depletion phenomenon of the perfluoropolyalkylether(PFPE) lubricant ZDOL caused by the head was investigated. FC722, a type ofpoly(fiuoroalkylmethacrylate) used as anti-wetting-agent (AWA) on the magnetic head, and its ef-fect on reducing lubricant depletion was study. Time-of-flight secondary ion mass spectrometer(TOF-SIMS) was used to characterize the lubricant ZDOL and AWA. TOF-SIMS results suggestthat the lubricant depletion should be due to dynamic friction between the magnetic head and diskduring the head flying or seeking over the disk surface, the amount of lubricant picked up by thehead varying with the different flying height. The AWA coating layer on head obviously reduces theamount of lubricant picked-up. The possible molecular interaction mechanics of AWA and ZDOLwith DLC overcoat of the head was discussed.
